Near field radio communications are increasingly being used for contactless data exchange, i.e. for Radio Frequency Identification (RFID) tags. RFID tags may be used for granting physical access to buildings and have even been embedded in identity documents such as passports. If a key, an identity document, or a financial instrument or credit card contains an RFID tag it is important to protect the data stored in the tag from unauthorized access. This can be achieved by providing access control to the device. For example passports control access by requiring the reader to optically read data from the passport which is then used in an access protocol. Alternatively one can radio-frequency (RF) shield an RFID tag when not in use. A card with an embedded RFID tag can be stored within an electrically conductive holder to provide RF shielding. For example, the U.S. Passport card does not have access control, but is distributed with a protective shield with a printed warning which advises the document holder to keep the passport card within the holder when not in use.
Near Field Communications (NFC) devices are active devices which communicate via high frequency, low range, near field radio waves. These devices can communicate with other NFC devices and may also assume the role of an RFID tag or reader.